The self-assembling nature and phase-transition behavior of a novel class of triarm, star-shaped polymer-peptide block copolymers synthesized by the combination of atom transfer radical polymerization and living ring-opening polymerization of alpha-amino acid-N-carboxyanhydride are demonstrated. The two-step synthesis strategy adopted here allows incorporating polypeptides into the usual synthetic polymers via an amido-amidate nickelacycle intermediate, which is used as the macroinitiator for the growth of poly(gamma-benzyl-L-glutamate). The characterization data are reported from analyses using gel permeation chromatography and infrared, H-1 NMR, and C-13 NMR spectroscopy. This synthetic scheme grants a facile way to prepare a wide range of polymer-peptide architectures with perfect microstructure control, preventing the formation of homopolypeptide contaminants. Studies regarding the supramolecular organization and phase-transition behavior of this class of polymer-block-polypeptide copolymers have been accomplished with X-ray diffraction, infrared spectroscopy, and thermal analyses. The conformational change of the peptide segment in the block copolymer has been investigated with variable-temperature infrared spectroscopy. (c) 2006 Wiley Periodicals, Inc.